1. Field of the Invention
The present invention relates to a coil unit for a motor stator and, more particularly, to a coil unit for reducing an axial height and a volume of a motor stator.
2. Description of the Related Art
FIG. 1 shows a conventional motor stator 8 including a plurality of silicon steel plates 81, two insulating sleeves 82, and a coil unit 83. Each silicon steel plate 81 includes a ring 811 and a plurality of supporting arms 812 extending radially outward from an outer periphery of the ring 811. A distal end of each supporting arm 812 forms a magnetic pole face 813. After the silicon steel plates 81 are stacked up, the insulating sleeves 82 are mounted to two ends of the stacked silicon steel plates 81. Each insulating sleeve 82 includes a plurality of extensions 821 corresponding to the supporting arms 812. The coil unit 83 includes a plurality of coils 831 wound around the respective supporting arms 812 and the respective extensions 821 to form the motor stator 8.
However, the stacked silicon steel plates 81 cause limitation to reduction in the axial height of the motor stator 8. Furthermore, the insulating sleeves 82 required for insulating and protecting the silicon steel plates 81 and the coil unit 83 result in an increase in the volume and the axial height of the motor stator 8. Further, the coils 831 wound around the supporting arms 812 and the extensions 821 also increase the axial height of the motor stator 8. Thus, when the motor stator 8 is utilized in a motor shown in FIG. 2, the total volume and the axial height of the motor can not be effectively reduced, leading to difficulties in miniaturization of the motor.
FIG. 3 shows another conventional motor stator 9 including a substrate 91 and a coil unit 92 comprising a plurality of coils 921 fixed to a side of the substrate 91. The silicon steel plates 81 and the insulating sleeves 82 of the motor stator 8 are not required, reducing the overall axial height and volume. However, the coils 921 of the coil unit 92 protruding beyond the side of the substrate 91 still has a certain height in the axial direction, leading to difficulties in reduction of the overall axial height of the motor stator 9 and in designs of compact and miniature motors.